ParameterNameDiscoverer implementation that tries to deduce parameter names
for an advice method from the pointcut expression, returning, and throwing clauses.
If an unambiguous interpretation is not available, it returns null.

This class interprets arguments in the following way:

If the first parameter of the method is of type JoinPoint
or ProceedingJoinPoint, it is assumed to be for passing
thisJoinPoint to the advice, and the parameter name will
be assigned the value "thisJoinPoint".

If the first parameter of the method is of type
JoinPoint.StaticPart, it is assumed to be for passing
"thisJoinPointStaticPart" to the advice, and the parameter name
will be assigned the value "thisJoinPointStaticPart".

If there remain unbound arguments, then the pointcut expression is
examined. Let a be the number of annotation-based pointcut
expressions (@annotation, @this, @target, @args,
@within, @withincode) that are used in binding form. Usage in
binding form has itself to be deduced: if the expression inside the
pointcut is a single string literal that meets Java variable name
conventions it is assumed to be a variable name. If a is
zero we proceed to the next stage. If a > 1 then an
AmbiguousBindingException is raised. If a == 1,
and there are no unbound arguments of type Annotation+,
then an IllegalArgumentException is raised. if there is
exactly one such argument, then the corresponding parameter name is
assigned the value from the pointcut expression.

If a returningName has been set, and there are no unbound arguments
then an IllegalArgumentException is raised. If there is
more than one unbound argument then an
AmbiguousBindingException is raised. If there is exactly
one unbound argument then the corresponding parameter name is assigned
the value <returningName>.

If there remain unbound arguments, then the pointcut expression is
examined once more for this, target, and
args pointcut expressions used in the binding form (binding
forms are deduced as described for the annotation based pointcuts). If
there remains more than one unbound argument of a primitive type (which
can only be bound in args) then an
AmbiguousBindingException is raised. If there is exactly
one argument of a primitive type, then if exactly one args
bound variable was found, we assign the corresponding parameter name
the variable name. If there were no args bound variables
found an IllegalStateException is raised. If there are
multiple args bound variables, an
AmbiguousBindingException is raised. At this point, if
there remains more than one unbound argument we raise an
AmbiguousBindingException. If there are no unbound arguments
remaining, we are done. If there is exactly one unbound argument
remaining, and only one candidate variable name unbound from
this, target, or args, it is
assigned as the corresponding parameter name. If there are multiple
possibilities, an AmbiguousBindingException is raised.

The behavior on raising an IllegalArgumentException or
AmbiguousBindingException is configurable to allow this discoverer
to be used as part of a chain-of-responsibility. By default the condition will
be logged and the getParameterNames(..) method will simply return
null. If the raiseExceptions
property is set to true, the conditions will be thrown as
IllegalArgumentException and AmbiguousBindingException,
respectively.

Was that perfectly clear? ;)

Short version: If an unambiguous binding can be deduced, then it is.
If the advice requirements cannot possibly be satisfied, then null
is returned. By setting the raiseExceptions
property to true, descriptive exceptions will be thrown instead of
returning null in the case that the parameter names cannot be discovered.